Document common violation of “EscapeSequence 0 [lookahead ∉ DecimalDigit]”

[mathiasbynens]

See https://mail.mozilla.org/pipermail/es-discuss/2013-June/031149.html and https://bugs.ecmascript.org/show_bug.cgi?id=1553. /cc @Constellation

[mathiasbynens]

Added some tests here: https://mathias.html5.org/tests/javascript/string/ (see the last two tests)

[mathiasbynens]

From https://bugs.ecmascript.org/show_bug.cgi?id=1553#c2:

Behaviour for noctal escapes in strict-mode is different across engines, e.g.
the proposed tests only work in V8 and Presto, other engines report a
strict-mode error (SpiderMonkey/JSC/IE).

EscapeSequence with leading "0":
- sloppy mode
=> accepted in major engines as "\08" == "\0" + "8"

- strict mode
=> accepted in V8/Presto as "\08" == "\0" + "8"
=> SyntaxError in IE/JSC/SpiderMonkey


EscapeSequence without leading "0":
- sloppy mode
=> accepted in major engines as "\8" == "8"

- strict mode
=> accepted in IE/SpiderMonkey/V8/Presto as "\8" == "8"
=> SyntaxError in JSC


OctalInteger
- sloppy mode
=> accepted in major engines as 08 == 8
=> Note: SpiderMonkey reports warning in shell

- strict mode
=> accepted in IE/Presto/JSC/V8 as 08 == 8
=> SyntaxError in SpiderMonkey

[mathiasbynens]

Ref. #9. https://mail.mozilla.org/pipermail/es-discuss/2013-March/029403.html